1. Field of the Invention
The present invention relates to an audio encoding device, an audio decoding device, an audio encoding method, and an audio decoding method that can encode and decode audio signals with high quality and at high speed.
2. Description of the Related Art
In audio communication conducted under conditions wherein the communication volume is limited, it is necessary to innovatively use audio signal encoding and decoding processing so as to communicate with the maximum audio quality achievable with a minimum of data.
One such direction of innovation involves effectively utilizing the characteristics of human hearing.
As one audio encoding method taking into consideration the characteristics of hearing, as described in for example in Japanese Unexamined Japanese Patent Application KOKAI Publication No. H7-46137 and JIS Std. No. JISX4323, methods are known wherein, after converting an audio signal into spectra, the spectra are separated into a plurality of sub-bands, while taking into consideration a critical region derived from the characteristics of hearing.
As a result, signal values, masking levels, noise, etc., for each of the above-described sub-bands are taken into consideration, and after calculating the number of bits necessary for encoding, encoding is conducted.
However, in such methods, the procedure for calculating the number of bits necessary for encoding is complex and requires many computational steps. In addition, there is also a problem in that calculating a masking level, for example, is non-trivial.
Therefore, the load on an encoding device executing computational processing becomes large, and there is a risk that the processing speed will slow. For example, in devices such as mobile phones, there is the possibility that bi-directional communication in real-time will become difficult. In order to avoid this, costs are unavoidably incurred because of the necessity of incorporating particularly high-performance calculating apparatus into encoding devices and the like.
Accordingly, there is a need for audio encoding devices and decoding devices that, while taking into consideration hearing characteristics, can communicate in real-time without any practical audio quality problems, using calculating apparatus wherein typical performance is sufficient.